Metal recovery from waste materials, by-products of manufacture processes, and ores is desirable for both the economic value of the metals contained therein but also for mitigation of liabilities attendant with disposal of potentially hazardous materials. Many of these are the transition elements (TE's). TE's are also referred to as transition metals and are any of the metallic elements that have an incomplete inner electron shell. Of particular interest are TE's selected from the group consisting of vanadium, molybdenum, iron, tungsten, cobalt and nickel. Numerous pyrometallurgical and hydrometallurgical processes have been devised in attempts to extract the metals with high rates of recovery and separate the metals into high-purity products. These processes are plagued by one or more deficiencies such as poor recovery rates, low product purity, high cost of chemical reagents, cumbersome chemical reactions requiring precise control, high capitalization costs for processing infrastructure or large quantities of environmentally hazardous aqueous waste products. Jones (U.S. Pat. No. 5,855,858) describes some of the deficiencies of known pyrometallurgical and hydrometallurgical processes.
There are distinct disadvantages to many known oxidation processes that rely on oxygen, chlorine, hydrogen chloride or other oxidants in the presence of strong acids, strong bases or other complex chemical mixtures to oxidize, dissolve and recover TE's as well as other components in aqueous media. There are also many disadvantages and inefficiencies to known processes that rely on ion-exchange resins, solvent extractions or electrowinning.
Oxidation by oxygen at elevated temperatures and/or pressures has long been known as a method whereby TE's can be converted to reactive chemical species amenable to additional chemical treatment and separation. However, oxidation in the presence of oxygen by known processes often does not quantitatively convert the TE's into reactive species that can be subsequently extracted.
For example, TE's with alumina (various crystalline structures of Al2O3) are difficult to recover due to the presence of refractory compounds and complexes containing TE's. One of the more common materials is an alumina-based catalyst with one or more TE metals deposited on alumina. The petroleum industry uses alumina-based catalysts referred to as ARDS, HDS, H-Oil, or RESID comprised of metallic Mo, Ni, Co, V and W singly or in combination on an alumina substrate. During high-temperature service, catalyst function decreases due to deposition of TE or other metals not in the original catalyst, formation of metal complexes, formation of metal-sulfur compounds, formation of TE aluminates, reduction in active surface area due to deposition of foreign materials such as hydrocarbons and unspecified poisoning of catalysis sites. Eventually the catalyst functionality is reduced to the point where it must be replaced with fresh catalyst.
Recovery of TE's from materials with alumina substrates by reaction with oxygen has been plagued by low recovery rates, principally attributed to the inability to break down Ni and Co aluminates, complex metal-sulfide compounds and other metal complexes. The dilemma is profound. The metal-sulfide compounds and complexes may be broken down at moderate temperatures; however, TE's, particularly Ni and Co, form refractory aluminates at about 1000° C. or higher and these refractory aluminates substantially reduce TE recovery rates.
Known processes teach that oxidative reactions utilizing oxygen typically are limited to <1000° C. U.S. Pat. No. 3,180,760 discloses a process for roasting alumina-based catalysts at 565-983 C. in air or O2 and then immediate treatment with sulfur, hydrogen sulfide, carbon disulfide or mercaptan to form reactive TE sulfides. U.S. Pat. No. 4,087,510 discloses roasting of alumina-base catalyst at 650-850° C. with caustic soda or sodium carbonate. U.S. Pat. No. 5,431,892 discloses roasting alumina-based catalyst at 400-<1000° C. followed by sulfuric acid and metal catalyst dissolution. Japanese patent JP-A-47-31892 discloses air oxidation prior to roasting with caustic soda or sodium carbonate. U.S. Pat. No. 4,292,282 discloses a process that includes initial oxidation at 650° C.-1000° C. and specifically recommends avoiding higher temperatures that form additional refractory cobalt aluminate. Japanese patents JP-A-47-21387, JP-A54-107801 and JP-A-51-73998 likewise disclose air oxidation. By limiting the temperature to <1000° C., formation of additional aluminates is minimized; however, subsequent extractions are either incapable of recovering metals, particularly Ni and Co, from refractory compounds or complexes or require dissolution of the alumina substrate in strong acids, bases or chemical mixtures to recover the TE's.
Oxidation of TE-bearing materials without an alumina substrate in an atmosphere containing oxygen at ambient pressure has been widely used as an initial processing step. However, oxidation with ambient air or O2 is seldom favored because of SO2 release and difficulties in recovering desirable metals from mixtures of TE oxides and undesirable element oxides. More frequently, pressurized O2 is used in conjunction with acidic aqueous phases such as in U.S. Pat. Nos. 4,384,940 and 5,855,858 to oxidize and leach TE-bearing materials. Contained metals are recovered through additional hydrometallurgical processing and/or electrowinning.
The volatility of TE chlorides, oxychlorides and partially hydrated oxychlorides are well known; however, little use has been made of their volatility in processing of TE-containing materials. U.S. Pat. No. 4,350,609 discloses a process for chlorinating calcined alumina-based catalyst with HCl and depositing MoO2Cl2 on fresh alumina to make new catalyst. French patent 724,905 discloses a process for chlorinating Mo, V and W on an alumina base in the presence of HCl or Cl2 and carbonaceous materials. TE chlorides are collected either by cooling or decomposition in H2O but are not separated.
U.S. Pat. No. 3,085,054 discloses a process for Ni—Co separation comprising dissolution of copper-nickel-cobalt sulfide matte in HCl solution at up to 65° C., extraction of Co with ion exchange resin or solvents, precipitation of Ni chloride from 7-9N HCl at ambient atmospheric pressure and recovery of Ni metal from a Ni chloride solution by electrowinning. Other known processes for separation of Ni and Co relate to methods utilizing various aspects of dissolution of materials in chemically complex acidic or ammoniacal ammonium sulfate solutions, solvent extraction, ion exchange resins, pyrometallurgy and electrowinning. U.S. Pat. No. 5,585,858 discloses limitations in some of these processes particularly as they relate to Ni and Co separation and recovery.
There is an industry need for a process to recover TE's that is characterized by high rates of recovery, high product purity, low net usage and the low cost of simple chemical reagents and relatively low quantities of useful or disposable waste. Furthermore, the processes should be amenable to extraction of TE's from a wide variety of materials comprising alumina-based materials, complex metal mattes, ores, manufacture waste or by-products and the like.